“File in use” message

Situation: Windows Server 2003 AD Domain, single server. All W/S’s are NT or XP. Clean Event Viewer.

Problem: One particular XP Pro user gets messages saying “Could not delete file. File is being used by another person or program”. Or words to that effect. File is located in server shared folder. Typically what he does is saves a file to the server from application (CadKey). Then exits CadKey, browses to the folder and renames the file. He then copies the same file from his workstation to the server by drag-n-drop. He then tries to delete the original file, and gets the error. Such as: Save file #1 to server. Rename #1 to #2. Copy #1 to server again using drag-n-drop. Try to delete #2 —> Error message. Eventually he CAN delete it but that’s not the issue.
Any ideas?

Brian